Operational limitations result in a certain amount of airspace to be protected. The exact dimensions of the area are variable. They depend upon the restrictions of the holding (altitude, outbound timing, VOR or NDB, DME, etc.). The basic shape is as shown above.
Obstacle clearance is 1000 ft (2000 ft over mountainous terrain). In a buffer area of 5 NM around the holding area obstacle clearance gradually reduces to zero.